Method of modulating ultra short waves



y 11, 1939- E. GERHARD 2,165,847

METHOD OF MODULATING ULTRA snow:- WAVES Filed June 13, 1936 2Sheets-Sheet 1 H. F. POWER INVENTOR ERNST GERHARD t MEANMLl/E awn/massBY g 4 ATTORN EY Patented July 11, 1939 UNITED STATES PATENT OFFICEMETHOD OF MODULATING ULTRA SHORT WAVES Ernst Gerhard, Berlin,

Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Eclegraphiein. b. 1-1., Berlin, Germany, a corporation of Germany 2 Claims.

The present invention is concerned with a modulation method for use withultra-short waves such as might be produced with a Barkhausen oscillatoror one with similar high frequency characteristics.

Various modulation methods have been disclosed in the prior art forultra-short waves. For instance, it has been suggested to modulateultra-short waves by radio-frequency energy i which, in turn, ismodulated by low frequency energy. In order to avoid distortions it isnecessary in all modulation methods known in the prior art to work upona rectilinear portion of the modulation characteristic. However, thestraight part of the characteristics happens to be very reduced in thecase of ultra-short wave generators in consequence of which only smallmodulation percentages are obtainable without distortion.

In describing my new method, reference will be made to the drawings inwhich curves or graphs referred to as Figures 1, 2, 3, 4, 4a, 5, and 5aillustrate the modulator characteristics and wave characteristics of theenergies used in my novel method and to Figure 6 which illustrates onecircuit arrangement including the main or principal elements forcarrying out the method of my invention.

Figure 1 shows, for instance, the modulation characteristic of anultra-short wave generator. N stands for the ultra-high frequency powerand U for the anode or other electrode potential of 'the generatortube.In Figure 2 is shown the identical modulation characteristic I. Thetransmitter radio frequency power in Figure 2 is to be modulated by thesinuous oscillation ii of lesser frequency. The resulting modulation ofthe ultra-high frequency power is shown in Figure 3. Curve 3 incomparison to the curve 11, of the modulating voltage, shown below inFigure 2, is entirely distorted. Such distortion could be avoided if theamplitude of the modulating frequency f1 were reduced to one-fourth, forin that case it would no longer go beyond the hump on the left-hand sideof the modulation characteristic l of Figure 2.

According to an embodiment of this invention the ultra-short waves whichI will refer to as is are acted upon by longer high frequency wavesreferred to as f2, which are, in turn, modulated by low frequency wavesor signal potentials T1, in such a way that during each half-period oralternation of the high frequency wave f2 one or two or a pluralityofenergy impulses of the ultra-high frequency is are produced whoseduration is a function of the amplitude of the radio frequencyoscillations f2, the maximum amplitude of the ultra-short waves f3being, however, in this scheme independent of the amplitude of the highfrequency f2.

Figures l and 5 illustrate the operation of the modulation method heredisclosed. The high frequency oscillation f2 in Figure 4 covers theentire modulation characteristic l of the ultra short wave generatorproducing frequency f3. In Figure 5 are shown the ensuing ultra-shortwave impulses l whose energy content is an inverse function of theamplitude of the high frequency f2. If the high frequency i2 is inaddition modulated by audio frequency potentials ii .i as indicated, forinstance, by line 5, in Figure 4, then also the median value of theultra-short wave energy pulses represented by curves t is subject to lowfrequency modulation. Thus, there results the median line 6 in Figure 5.Inasmuch as in this arrangement the ultra-short wave energy is becomesless as amplitude of the high frequency energy f2 increases, the lowfrequency or signal modulation of the radio frequency wave f2 must becontrolled in a negative sense by the modulating potentials f2, in otherwords, the amplitudes of the high frequency f2 must be so much lower,the greater the audio frequency potential. This is indicated by lines 5of Figure 4 which indicate modulation of a e small number of cycles off2. Nevertheless the lowest amplitudes of f2 modulate f3 throughout itsentire range. This desired relation between the amplitude of the audiofrequency potentials and the amplitude of f2 may be obtained by properlyconnecting the circuit leads such as those to the modulation transformeror reversing said leads if they are not connected in the proper sense,or by other similar expedients. When the connections are proper theaudio frequency en- 40 velope of the modulated carrier f2 is reversed,and when the signal is positive more energy will be radiated than on thenegative half, as shown by Figure 5. Thus both positive and negativehalves of the signal are useful in controlling the carrier energy. Onthe negative half of the signal f2 is larger in amplitude and hence theenergy content of is is correspondingly smaller. The audio frequencymodulation of the ultrashort waves is is entirely independent of theshape of the modulation characteristic I of the ultra-short wavegenerator. If f2 were of small amplitude relative to the full modulationrange then is would vary in amplitude between a fixed upper limit andsome lower value. If f2 has an iii) amplitude that is equal to orgreater than the modulation range through which is can be modulated, andit has, as indicated in Figure 4, the power output is is zero (tube cutoff) except for a small portion of the cycle (f2) which lies within themodulation range of voltages. This portion of the cycle of f2 at whichis is cut off becomes larger as f2 increases and vice versa. This isshown in Figure 5 where-the amplitudes of the envelopes of is areconstant and the narrowest f3 power graphs designate the higher isamplitudes where the periods of time is is cut off by T2 are longest. Inother words, the basic idea of this invention will be useful wherever amodulation characteristic comprises such a reduced linear portion thatthe percentage modulation would be very low in the conventional workingmethods if distortion is to be avoided. In other words, the chief fieldsof use are with Habann tubes, magnetrons, and the like.

.By reducing the normal direct current potential on which the modulatedhigh frequency modulating wave [2 is superposed the is output may bemade linear in amplitude and power with respect to the audio frequencyinput. This method of operation is illustrated in the curves of Figures4a and 5a. Here negative modulation of is is not necessary.

In Figure 6 which illustrates a circuit arrangement for'carrying out theinvention, modulating potentials from 59 act through modulationamplifier l2 and transformer M to modulate oscillator l6. It; mayproduce oscillations of a frequency f2. The output of It modulates theultra-high frequency oscillator l8 by controlling the potential suppliedto an electrode of a tube generator therein. This electrode may be thegrid in the case of Barkhausen oscillators, or the anode. As pointed outhereinbefore, other types of oscillators such as a magnetron oscillator,or dynatron, or any oscillator having as a characteristic feature anoscillatory power output which ceases when the supply voltage exceeds acertain value may be used at i8. it; may generate a frequency fa whichwhen modulated is supplied to any utilization circuit. To operate thecircuit of Figure 6 in accordance with the method illustratedgraphically in Figures 4 and 5 the normal potential on IS establishes anormal ultra high frequency carrier is. Now when f2 is impressed from !6on I8 the output of i8 is reduced for each half period of the wave. Iff: is of very small amplitude relative to the range of potentials thatare to be applied to the modulator stage IS without reducing the outputof the same to zero, is will merely vary in amplitude between a fixedupper limit and some lower value as shown in Figure 3. However, if f2has a much larger amplitude as shown in Figure 4, the output of I8 (is)is modulated to zero except for a portion of the cycle of 1'2 which lieswithin the range of voltages insufiicient to modulate 58 to zero output.The duration of f2 voltages insufficient to modulate I8 (is) to zero isgreatest for the lower values of f2. See Figures 4 and 5. And decreasesas the amplitudes of f2 increase so that for smaller values of f2 we getlarger output (energy content of is) from l8 and for larger values of f2smaller output from l8. This has been shown graphically in Figure 5wherein the narrowest power graphs indicate the higher amplitudes of f2.

However, the idea underlying the invention is not exhausted by theexemplified embodiments here shown.

I claim:

1. The method of signallingvby means of ultra high frequencyoscillations, oscillations of lower frequency and of amplitude which isgreat relative to the amplitude of said ultra high frequencyoscillations and voltages which vary at signal frequency which. includesthe steps of, modulating said oscillations of lower frequency in anegative sense in accordance with said voltages of signal frequency, andimpressing said modulated oscillations of lower frequency on said ultrahigh frequency oscillations to interrupt the flow thereof during aportion of each cycle of the modulated oscillations of lower frequencywhich is a function of the amplitude of the modulated oscillations oflower frequency.

2. The method of signaling by means of ultrahigh frequency waves whichconsists in, producing a'relativelylow frequency oscillatory voltage,modulating the amplitude of said voltage in accordance with signalpotentials, superimposing said modulated relatively low frequencyoscillatory voltage on a direct current voltage and generating, by meansof said superimposed voltages, ultra-high frequency oscillations toproduce an ultra-high frequency power output which increases frcm zeroto a maximum and back again to zero as the superimposed voltagesincrease from a first value to a second value, the unmodulated amplitudeof said relatively low frequency oscillatory voltage being greater thanhalf the difference between said. first and second values at all phasesof the cycle of modulation of said relatively low frequency oscillatoryvoltage by said signal potential.

ERNST GERHARD.

